1. Field
The present disclosure relates generally to communication systems, and more particularly, to improving coexistence of synchronous and asynchronous nodes in a synchronous MAC system.
2. Background
In various communications systems, carrier sensing alone or in combination with a randomized backoff transmission time technique is used to determine when a device will transmit on a physical communications channel. In a typical 802.11 based system, a broadcast packet is transmitted on a channel based on a distributed coordination function (DCF) mechanism. The system may include multiple nodes.
For broadcasting messages, 802.11 CSMA based media access control (MAC) lead to poor performance at high node density, due in part to packet reception collisions. Where a synchronous MAC is introduced, nodes with access to GPS or other timing signals may only attempt to transmit at a given slot boundary. The said slot is further selected from a plurality of possible slots based on the interference measured at each slot (e.g. a node may pick a slot with the least amount of interference). This kind of simple synchronous MAC allows for maximizing geometrical separation between nodes transmitting at the same slot and thus improves the overall system performance.
However, if only a fraction of the nodes are enabled with this synchronous MAC slot timing scheme, the performance of the overall system deteriorates as the number of legacy nodes increases. This is because a node that starts transmitting in the middle of a slot can cause a snow-ball effect to the other nodes which eventually may destroy the structure formed in the synchronous MAC.
Therefore, there is a need in the art for improving the performance of the synchronous MAC in the presence of legacy nodes while minimizing an overall performance reduction to a synchronous MAC system.